Method and Apparatus for a Fast Installation of an IP User Connection over a 3GPP Nb Interface under Application of the BICC “Delayed Backward Bearer Establishment” and Avoidance of Failure.
The “Nb Framing Protocol”, standardized in 3GPP TS 29.415, is used for the transport of user data in the “Cs Domain” of a 3GPP mobile network. The Nb framing protocol also features inband signaling messages, for instance an Initialization message and an Initialization Acknowledge message. The inband signaling messages need to be exchanged prior to any user data. The ITU-T standardized “Bearer Independent Call Control” (BICC) Protocol, ITU-T Q.1902.5, is used for the so-called Call Control Signaling, as described in 3GPP TS 23.205.
In the case of the use of the IP Protocol for the transport of the User data over the “Nb” interface in the core network of the Cs Domain, the IP addresses and UDP port numbers used to send and receive transport connections at “Media Gateways” (MGW) or integrated “Mobile Services Switching Centers” (MSC) are negotiated with the help of “IP Bearer Control Protocol” (IPBCP), ITU-T Q.1970, as specified in 3GPP TS 29.414. The MGW and integrated MSC connect the function of the MGW and “MSC server” in one device.
The BICC protocol provides different methods for the setting up of IP transport connections, among them the so called “Delayed the Backward Bearer establishment”, that is the delayed backwards-directed establishment of the transport connection. In this case, with respect to the initialization of the Nb Framing Protocol, the following problems are still unresolved.
An MGW O sends towards the next MGW T in the direction of the callee, that is called party, an IBCP Accepted message with the IP address and the UDP port number, which the MGW O selected for sending and receiving the user connection. The MGW O simultaneously or soon afterwards sends an initialization message of the Nb Framing Protocol towards MGW T. It is necessary that the MGW T answers the Nb Framing Protocol initialization message immediately with an initialization answer message to the MGW O, in order to achieve a fast establishment of the user connection in order to prevent that the MGW O regards the lack of the answer message during a certain period, as an error case. In accordance with the existing standard, MGW T must send the initialization answer message to the IP address and UDP port number of the MGW O indicated in the IPBCP Accepted message.
The MGW O sends the initialization message of the Nb Framing Protocol directly by means of IP towards the MGW T. On the other hand, the MSC-O sends the IPBCP Accepted message to the MSC Server 0, controlling it. Next, the MSC Server 0 forwards the IPBCP message by means of the BICC call control signaling to the MSC server T controlling MGW T, which passes the message on to MGW T. Therefore, it is likely in this scenario that the initialization message of the Nb Framing Protocol MGW T reaches its destination distinctly before the IPBCP Accepted message.
Problematically, the behavior of the MGW T in this situation is not heretofore recognized in the standard. As a result, the MGW T could ignore the still unexpected initialization message of the Nb Framing Protocol and/or assume an error case and break off the connection establishment. The MGW T might also continue to wait for the IPBCP Accepted message, that is before sending the initialization answer message, which can lead to delays of the installation of the transport connection and errors in the MGW O.